A variety of mold assemblies are currently available for the molding of articles from materials cured by the control of temperature and pressure. In the past, mold assemblies have consisted of single or multiple cavity, multiple plate molds. The molds were generally pre-heated to a desired temperature, clamped or compressed by an injection mold machine, and then injected with the desired molding material. The injection of the molding material was often accomplished using a injection press. The molding material in the cavity or cavities of the molds was then cured under pressure within the injection press.
The production rate of injection molded articles in molding systems using mold assemblies of the type mentioned above has been increased by the use of conveyors to transport the molds between injection, compression, and heating stations. For example, U.S. Pat. No. 1,935,794 provides a method of molding articles in which the mold is transported by a transfer system between a heating station and a compression station, and maintained under compression during transport through a curing station.
A disadvantage, specifically with respect to molding systems using an injection system having in injection press to apply continued pressure to the mold during both injection and curing of the material, is that the injection press is primarily utilized as a press, rather than as an injector. The use of an expensive injection press for providing pressure to the mold, rather than solely for the injection of material is inefficient, and reduces the overall cost effectiveness of the system.
Another disadvantage of molding systems using past mold assemblies is the high forces or clamping forces required to be applied by the injection system to resist both the operating pressure externally applied to the mold during the injection of material into the mold, and a separation pressure internally applied to the mold as a result of the injection of material and initial curing of the material within the mold. The component of the separation pressure attributed to the injection of material is proportional to the cross-sectional area of the molding cavity. The clamping or resistance force required must be greater than the operating and separation pressures. Thus, as the size of the product to be molded increases, the clamping force required to be applied also increases.
With conventional molds, the separation force generated is a function of the entire exposed or unloaded components forming the internal mold cavity, or the cross-sectional area of the mold cavity. With a self-clamping mold, however, the separation force is only a function of the exposed portions of the mold, and the cross-sectional area of the runners and sprue openings. Thus, prior mold devices required larger clamping forces to be applied by the press, since the molds were not pre-loaded.
A still further disadvantage of conventional molding systems is that the molded articles produced typically require additional processing to remove flash from the articles. The formation of flash, and its removal, result in increased costs due to wasted material, and the additional process of deflashing the article, or removing the excess material, and finishing the article. An additional inspection of each article may also be required, which further increases the overall labor expense of the system.